CA1153818A - Versatile microsecond multiple framing camera - Google Patents

Abstract

VERSATILE MICROSECOND MULTIPLE FRAMING CAMERA

Abstract of the Disclosure A versatile microsecond multiple framing camera generates a switched beam of illumination derived from a laser and switched by an acousto-optic modulator. The illumi-nation is focused on a subject, and illumination from the subject is caused to scan over a predetermined field by a mechanical or electromechanical scanner.
Located in the field is an image recording device for recording the illumination directed over the field by the scanner. The image recording device, in one embodi-ment, includes a vidicon tube, for short term storage, and a video recorder for longer term storage. A video monitor may be driven from the video recorder. The versatility of the camera is exemplified by the ability to vary exposure times or frame rates by adjusting operator controls which drive the acousto-optic modula-tor and/or the electromechanical scanner. In other embodiments, the vidicon tube and video recorder can be replaced or supplemented by photographic film.

Description

1~5~8 VERSATILE MICROSECOND MULTIPLE FR~ING CAMERA

Field of the Invention -The present invention relates to devices for recording visual images, and more particularly, images of events whose time duration may be on the order of microseconds.

Background of the Invention In many fields of endea~or, the ability to record visual images plays a significant part. Prior art devices for recording visual images are available in the form of devices which employ photographic film, and electronic devices for recording visual images such as the conventional TV camera, or more precisely, a vidicon tube, for example.

Essential to the production of a useful visual image is sufficient illumination intensity. The advent or the laser, with its intense output, has enabled the re-cording of events whose time duration is in the micro-second range, or less.

Some examples of visual recording devices employing laser illumination sources include Armstrong et al, U.S. Patent 3,445,167; Guillet et al, U.S. Patent 3,643,568; McCall, ~.S. Patent 3,485,159; and some of the cameras described in Huston's "High-Speed Photography and Photonic Recording" appearing in J. Phys. E:Sci.
Instrum. Vol. 11, 1978, pages 601-609.

These and other prior art cameras employ a variety of techniques to record information on a visual record.
For example, Huston discusses framing photography which produces one or more two-dimensional images of the subject, a species of framing photogr2phy is entitled multiple framing photographywhere a short sequence of YO97~-079 ~'38~8 two-dimensional images is recorded in such a way that it is not possible to project the result as a conventional movie -type presentation. He also discusses the conven-tional movie-type photography which produces a sequence of two-dimensional images so that projection can take place at a slower rate. In addition, streak photography dispenses with one spatial dimension and records, without interruption, the time variations of the image with respect to a single dimension only. Another technique employed in photography in general as well as in microsecond photography, is stroboscopic photography in which multiple images of a subject undergoing a periodic process are recorded at the same relative time into the process. Each of these techniques carries wi~h it different requirements for illuminating the subject, processing the illumination from the subject and recording the same. Depending upon the particular type of equipment used to record the image, various changes must be made to adapt the equipment to operate under the different regimes.

Furthermore, and especially significant in micro-second photography, is the necessity for the equipment to be precisely timed with respect tothe events sought to be recorded. The changes necessary in the recording ~5 equipment to effect this precise timing, for photographing different events or different occurrences of similar events, requires more or less effort depending upon the particular equipment employed, and the techniques that equipment employs to record the image.

- 30 It is one object of the present invention to provide a camera capable of effecting microsecond photography which is not only versatile in that essentially the same equipment can be employed to generate multiple framing photography, streak photography and stroboscopic photo-~5 .~8~
1 graphy, but is also relatively simple to altex from one regime to the next. It is another object of the present invention to provide a microsecond photography camera which is easily adjustable to capture precisely the images sought to be recorded, when those images may exist for time durations on the order of a microsecond, or less. It is another object of the present invention to provide a microcecond photography camera which is relatively simple to adjust in that the parameters whose adjustment is required to achieve the desired result, are easily controlled. These and other objects are met in accordance with the invention which will now be described below.
Summary of the Tnvention In accordance with the invention, a microsecond multiple framing camera includes an intense, switched source of illumination, focusing means for focusing the illumination on the subject, a mechanical or electromechanical scanner for redirecting illumination from the subject to sweep over a field as a function of time so as to distribute multiple images over the field, and an illumination recording device located in the field in which the illumination is swept by the mechanical scanner for recording illuminaticn. A
control device for driving the switched source at a selected duty cycle and repetition rate is gated on in response to the position of the electromechanical scanner. The duty cycle and repetition rate may be operator-selected parameters to determine exposure time and the number of frames in each field.
More particularly, the switched high intensity illumina-tion source may comprise a laser and an acousto-optic modulator. With the laser continuously energized, ~5~3818 operation of the modulator can produce a switched illumi-nation beam. Conventional acousto-optic modulators now available allow the modulator to go from an off state to an on state and back to the off state in O.l~s. The electromechanical scanner may comprise a galvanometer or resonant electromechanical scanner which comprises an electromechanical coil driving a reflector such that as the reflector is driven, illumination from the subject is caused to sweep over a predetermined field in space.
The recording device is located in the field of space through which the illumination from the scanner is swept, and that device may comprise a vidicon tube for short term storage (i.e. r on the order of 17 milliseconds) of an image coupled to a video recorder for long term storage of ~e image.

Proper inter-relationship between the exposure time which is determined by the on state of the acousto-optic modulator, the velocity of the scanner, and the area of the field through which it scans enables multiple framing photography to take place. More particularly, the acousto-optic modulator control is gated on at a con-venient time, such as when the scanner is in a position to reflect illumination to a predetermined portion of the field. The acousto-optic modulator control turns the modulator on for a selected time duration, selected so that the on time is short relative to the velocity of the scanner to, in effect, "freeze" the image, thus, creating a frame or distinct image of the event. The acousto-optical modulator is then disabled for a sufficiently long time so that when it is again enabled, the scanner has moved through a sufficient angle so that a second image can be recorded in the field at a location displaced from the recording location of the first image.
The acousto-optic modulator is then enabled for an ~S,~ 8 equivalent short period of time to again "freeze" the second image. Preferably, the inter-frame time, that is, the time during which the acousto-optic modulator is off, is at least 10 times the duration of each ex-posure, which is determined by the time during whichthe acousto-optic modulator is on. The inter-frame time can, of course, be much larger than the exposure time, depending on the desired result. For example, the inter-frame time can be lOOO~sec.

The control device for controlling the acousto-optic modulator can comprise simple electronic gating and time delay circuits whose parameters are easily varied by an operator to achieve the precise timing of the camera required for this type of photography, as well as for altering the photography technique employed from multiple framing to streak or stroboscopic. In addition to controlling the acousto-optic modulator, the control device can either respond to scanner position, or actually control scanner movement itself depending upon the particular events sought to be recorded.

To assist the operator in adjusting the various para-meters, video monitor may be employed in connection with the video recorder so that, essentially, "real time" information is available to the operator with 2S respect to the accuracy of his adjustments in order to achieve the desired effects. A video monitor may be replaced by a simple viewing screen and appropriate optical components to throw a representation of the image onto the screen to assistthe operator. In addition, the entire vidicon/recorder/monitor can either be replaced or supplemen~ed with photographic film and the necessary optical components to throw an image of the subject on the film plane to obtain high~resolution Y097~-079 than that which i5 possible with the vidicon.

For the purpose of this application, the phrase "micro-second camera" should be understood to include a camera capable of capturing images whose duration is on the order of 1~ sec or less, although the camera has applications in which the images capaured may be of longer duration, as is explained below.

In view of the foregoing, it should be apparent that one aspect of the invention includes a versatile cal-nera for recording plural framesof an image in which is readily controlled and in which the camera includes:

a switched laser source means for producing a switched beam of illumination, focusing means for focusing the illumination on a subject, mechanical scanner means for redirecting illumination from the subject to sweep over a field, illumination recording means located in the field for recording illumination from said mechanical scanner means, and control means responsive to said mechanical scanner means for controlling said switched laser source means, Brief Description of the Drawings In the accompanying figures, like reference characters identify identical apparatus and Figure 1 is a block diagram of the inventive camera;

Yo97s-o~g .8 Figures 2A and 2B show light pulses and scanner deflec--tion as a function of time;

Figure 3 is a part block, part schematic diagram of a preferred em~odimenti Figure 4 is a block diagram of an element of the inven-tive camera;

Figure 5 is a part block, part schematic diagram of another embodiment, and Figure 6 is a schematic showing generation of the scanner position signal.

Detailed Description of Preferred Embodiments Figure 1 is a block diagram illustrating the inventiye microsecond camera. As shown in Figure 1, a switched light source lQ produces an intense beam of illumination which is switched on and off by a control device 11. Both the duration of the on time of the illumination beam, as well as the off time, are controlled, for reasons which will appear hereinafter. A lens system 12 focuses the beam onto a subject 13. Illumination from the subject 13 is passed through objective lens 12' and is directed to a mechanical scanner 14. Operation of the mechanical scanner causes the illumination from the subject 13 to scan a field 15. An image recorder 16 is provided for retention of the image painted on the field 15 by operation of the scanner 14. In addition, and desirably, a monitor 17 may respond to the image recorder 16 so as to provide the operator with substantially an instantaneous image of the recorded image. In order to coordinate the on times of the switched source 10 with the position of the scanner 14, the control device 11 responds tothe scanner 14 in order to control the on periods of the illumination source 10. In those cases where the subject to be viewed undergoes a short term process, the control 11 may also provide a signal to trigger the subject process. For example, the inventive camera has been used to record ink droplets, from an ink jet printer, striking a surface.
Thus, the trigger signal can be used to start the process of emitting ink from the printer. The operator can intelligently operate the control device 11 by viewing the results of previous operations on the monitor 17.

Figure 2 illustrates one desirable relationship be-tween scanner position and operation of the switched source. In Figure 2A, scanner position is plotted as a function of time. At any instant of time, the position of image in the field 15 is determined by the lS position of the scanner 14. Accordingly, the switched source 10 is controlled to produce a periodic stream of illumination beams, or a pulsed beam, at a controlled repetition rate, and with a controlled delay between ; individual pulses as shown in Figure 2B. For each illumination beam, A through K, for example, occurring during a single sweep of the scanner 14, a different image of the subject 13 will be produced in the field 15, and since the different illumination pulses from the source lO-are time displaced, so, too, will the various images be space displaced in the field 15 so that each is separately viewable in a pre-determined order. While the scanner motion can be of the triangular waveform shown in Figure 2A, that is not essential to the invention, so long as a portion of scanner motion is of the form shown in Figure 2A.
While Figure 2A illustrates that scanner position is a linear function of time, for at least the portion of the scanner movement illustrated, that is only a desir-able goal and not essential to the invention. The ~i?~

g displacement between adjacent illumination beams or pulses must be sufficiently lon~, in connection with the scanner movement, so that images produced by the respec-tive beams will be spatially displaced in the field so that they can be independently viewed.

Several other constraints are imposed upon the form of the switching waveform. Namely, the on time of the source, when considered in connection with the intensity of the source, must provide for sufficient energy so that the recording device can respond. At the same time, the on time must be sufficiently short, when considered in connection with the velocity of the scanner 14, so that image smear is not produced, i.e., the on time should be short enough to "freezel' any motion occurring in the subject 13. Finally, the displacement between adjacent illumination pulses, considered in connection with the velocity of the scanner 14, must be sufficiently great so that the images produced on the field 15 will not overlap.

In a preferred embodiment of the invention, the source comprises a helium neon laser (although obviously other lasers could also be employed) and in one experiment, the on time of the illuminatlon pulse was on the order of l/lOth of a microsecond. The off time of the source is preferably at least 10 times the on time, although the only upper limit on the off time is a desire to record several images during the time of a single scan of the field 15 by the scanner 14. Thus, for example, the inter-frame time could vary from 1 to 103~ sec., and with a time for exposing an entire field varying from 3 to about 105 ~sec. with as few as 3 to 100 imaqes or frames per field.

Y097~-0/9 ~igure 3 is a schematic illustration of a preferred embodiment. ~s shown in Figure 3, the output of a helium neon laser 20 impinges on an acousto-optic modula-tor 21.
The beam passes through the acousto-optic modulator 21 but the position of the beam at an aperture 22 deter-mines whether or not the illumination will pass the aperture 22. Thus, for example, when the acousto-optic modulator is driven on by an electric signal, the beam is displaced to pass a first order maximum through an aperture 23; when the acousto-optic modulator 21 is not driven, the beam is blocked hy the light block at 24.
Accordingly, driving the acousto-optic modulator 21 produces an illumination pulse which terminates when the acousto-optic modulator 21 is not ariven. ln the preferred embodiment of Figure 3, the lens system 12, 12' comprises condenser lenses 25 and 26 and an objec-tive lens 27 forming an open-air microscope. In the referred to ink jet experiment, the condenser lenses 25, 26 were selected to give a cigar-shaped image (longer than wide) on the field 31 by use of a cylindrical element. The lenses 25 and 26 focus the illumination pulse on a subject 13 and the illumination from the subject 13 passes through the objective lens 27 where it strikes a reflector R of the scanner 14.
To ensure adequate response of the modulator ~i.e., less than 0.4~sec.), the lens 20a is of a 1 m. focal length so beam diameter is much less than 1 mm. The reflector R is driven by the scanner 14 to descxibe cyclical movement about its axis 28. The scanner 14 provides a signal to the control device 11 periodically in the cycle of scanner movement, for example, when the scanner passes a predetermined position or angular displacement from its rest position. The illumination pulse reflected by the reflector R can be imaged directly on a field 15 in which case the images are displaced in one direction as the reflector R moves ~53~3~ 8 through its arc. Figure 3, however, illustrates a technique whereby two displaced series of images can be produced in a single field 15 during a single scan of the reflector P~. As shown in Figure 3, a first mirror 29 is oriented so that illumination pulses re-flected by the reflector R during the first portion of its scanning movement result in a vertically displaced series of images in the portion 29' of the field 15.
As the reflector R continues its rotation movement in a second portion of its scan, the illumination pulses are directed at a mirror 30, whose orientation is slightly different from the mirror 29. Accordingly, the illumi-nation pulses reflected by the reflector 30, as the reflector R scans the second portion of its cycle, produces another vertically displaced series of images in the portion 30' of the field 15 which another series of images is horizontally displaced from the series of images 29'. Obviously, more than two distinguishable portions of the scan of the reflector R can be selected by multiplying the number of mirrors 29 or 30, at various orientations, so that the field 15 is, in effect, broken up into a like number of portions.

The principle of operation of an acousto-optical modu-lator is discussed in "Modulators for Optical Communica-tions" by Chen, appearing in Proceedings of the IEEE, Vol. 58, pages 1440-1447 (October 1970); ~. V. ~ance and J. K. Parks ~ r'Wide Band Modulation of a Laser Beam, Using Bragg-Angle Diffraction by Amplitude-~odulated Ultra-Sonic Wave" in the Journal of Acoustical Society of America, Vol. 33, pages 14-23, July 1965; and, D.
Mayden "Acoustico-Optical Pulse Modulator" in the IEEE
Journal of Quantum Electronics. Vol. QE-6, p. 15-24, January 1970. As employed in the inventive camera, the modulator 21 is arranged to pass illumination from the ~53~8 -12~
the laser into a light block 24 when the modulator is not energized. When a pulse from control 11 is re-ceived, the modulator 21 deflects the beam to pass a first order maximum through aperture 23. The modulator should result in a black/white ratio of at least 102, although at least 103 or 104 is preferred.

Electromechanical scanners are actually commercially available devices from either Electronics Division of Bulova Watch Company, Inc., Woodside, New York, or General Scanning Corporation, Watertown, Massachusetts. Of the commercially available devices, those suitable for use in the inventive camera are either of the galvanometer or resonant type. In the former, a galvanometer type movement is arranged to rotate a reflector, feedbac~
circuitry provides excellent linearity between the driving waveform and reflector deflection. The reflec-tor can be deflected up to 60 peak to peak, and the driving frequency can be in the range between zero and 25 kHz., usually, however, as the freauency of the driving function is increased, the arc through which the reflector is driven decreases. Typical resonant devices mount the reflector either on a torsion rod or a taut band, and depending on the type of mounting, may achieve up to 30 peak to peak deflection, at fre-quencies from very low to more than 20 kHz., although as the frequency is increased, the deflection angle isreduced.

Because of the linearity in galvanometer rotation and driving waveform, ~e driving waveform itself can be used as an indication of scanner position. A simple comparator (60 in Figure 5) is arranged to emit a pulse at the desired point in the waveform, which can be selected by merely selecting the reference input (~ef.) to the comparator 60 by appropriately positioning the poten-tiometer P.

Pesonant scanners have a pick-up coil from which a signal related to scanner position is available. With a suitable comparator 60, a pulse or spike can be gen-erated when the scanner is in a position corresponding to the reference signal.

In the ink jet experiment referred to, the effective distance from scanner to vidicon was about 30", so the 1" vidicon screen was covered by scanner rotation through 0.9 resulting in the beam being swept across 1.8. In the same experiment, the delay used by a delay circuit 34 was lOO~sec. with a O.l~sec. exposure and a lo~sec delay between pulses, so that 10 frames were produced 100 200A~sec after the ink jet was triggered.

As shown in the embodiment of Figure 3, the image re-cording device 16 comprises a vidicon tube or the like 31, a video recorder 32 with a stop action capability, responsive to the vidicon tube 31 and optionally, a television monitor 33 responsive to the video recorder 32. Figure 3 shows the monitor 33 with two vertically displaced sets of four images.

Typically, the vidicon tube 31 (or other equivalent TV
camera) will read out its screen every 17 ms., although it is capable of storing images for up to -1 sec., if not read. Even when read, the image is not erased, but only reduced in intensity. Thus, the vidicon is essentially a short term storage device which can easily store multiple images (2 - 60 or more) each time dis-placed from its neighbor by 1-103~sec. until it is read ~538~8 out for permanent recording. While the video recorder 32 can use a tape medium, conventionally, resolution is diminished. Storage without degradation in resolution can be effected by using a digital storage with a disk medium. ~Tsually, ambient light is not a problem, but if high intensity room light must be tolerated, a 6328 A
interference filter can be placed in front of the vidicon.

Figure 4 illustrates the control device 11. As shown in Figure 4, the scanner position indicating signal is pro-vided as an input to an operator adjustable time delay circuit 34. One output of the time delay circuit 34 is a short pulse delayed from the input by the operator selected amount. This is coupled to a pulse stretching circuit 35 which may comprise an operator controlled mono-stable multivibrator. The output of the pulse stretchingcircuit comprises a pulse beginning at the time of the input, and having a duration selected by operator control.
The output of the pulse stretcher 35 is coupled to a gated squarewave generator 36. The output of the gated square-wave generator 36 is a series of pulses of predetermined duration and repetition rate, the entire series of which is gated by the output of the pulse stretcher 35. The output of the gated squarewave generator 36 is coupled to the acousto-optical modulator 21, wherein each pulse rep-resents an on state of the modulatorr and the off period of the pulses relate to the off state of the modulator.
The other output of the time delay 34 is an undelayed spike which can be used to trigger the subject. Although the control device 11 can be built of off-the-shelf com-ponents~ the delay 34 and pulse stretcher 35 can comprise, ` respectively, the "A" and "s" time bases of a ~od 545 Tektronix oscilloscope, which is commercially available.

In typical operation, each pulse from the gated s~uare-wave generator is on for 0.1 microseconds, the delay be-tween plllses can be anywhere from 1 to 1000 microseconds Yn97~--n74 ~l~S-~8~8 or more~ A typical vidicon tube is "read" every 17 milliseconds in interlaced fashion so that two consecu-tive video fields correspond to a video frame; and the frame has a duration of about 34 milliseconds.

Assume that a subject sought to be recorded exhibits motion which is of interest over a period of 500 micro-seconds, at some undefined but repeatable time in the range of 100 to 2500 microseconds after it is energized.
The inventive camera can be used to capture a sequence of images in the range of 3 to 64, for example, existing over the duration of the 500 microseconds of interest, in the following fashion.

The scanner is initiated into motion which has a linear or quasi-linear displacement as it sweeps illumination from the subject over the field. The arc through which the scanner swings,the distance to vidicon 31 and the preqence of rèflectors in that path are selected so the linear or quasi-linear swing of the scanner covers the active area of the vidicon 31. The operator selects the delay provided by the delay circuit 34 somewhere in the range of 100 to 2500 microseconds, selects the period of the pulse stretcher to be 500 microseconds and selects the period between the pulses provided by the squarewave generator so that the off time is equally distributed between the number of frames that are to be recorded in the 500 microsecond period. For example, if 50 frames were to be recorded, the off period would be selecte~ as a~outlO microseconds. The subject sought to be photographed is then energized or released and the resulting image is examined on the monitor. Since the operator can only "capture" a 500 microsecond time slice, the time slice actually captured may be either before, after, or partially overlapping the subject's activity of interest. By adjusting the delay pro-YO97~-079 ':' .8 vided by the delay circuit 34, the operator can zero in on the desired time slice. In the alternative, the period of the pulse stretcher 35 can be selected to cover an entire video frame, i.e., 35 milliseconds. In this case, while very little video information will be obtained, since the entire activity of interest will be compressed into l/7th of the video frame (i.e., 3500 divided by 500) the location at which it appears will provide an operator with information as to what the delay of the delay circuit 34 should be to properly photograph the activity desired. In this fashion, the operator can rapidly and precisely select the desired parameters of the camera so as to view in an optimum fashion the activity of interest.

The foregoing discussion has assumed that the image sought to be recorded employed transmitted light so that the image actually recorded corresponds to a silhouette type record. However, that is not essential to the invention, and by merely varying the relative locations of the scanner and the subject, scattered light could be employed to create the image for recording. A
particular difficulty with scattered light photography is the low collection efficiency of the objective lens.
For example, using transmitted light photography, a l milliwatt helium neon laser produces acceptable results at exposure durations of 3/lOthSof a microsecond or greater. If the same l milliwatt laser is to be used for scattered light photography, the exposure time should be increased to be greater than lO microseconds, and correspondingly, the inter-frame time should be lengthened to at least lOO microseconds. In the aïternative, how-ever, by increasing laser power, for example, to the 0.1 to l watt range (corresponding to the use of an ion laser~ the exposure time of 0.1 microseconds can be main-Y0978-07~

~L~538~8 tained. Intermediate values would be to employ a lO
milliwatt laser, use an exposure time of about l micro-second and inter-frame times of about lO microseconds.

The present camera can also be employed to produce streak photography by firstly using a slit at the microscope entrance (i.e., before the condenser lens) as is conven-tional in streak photography, and by lengthening the on time of each pulse in the gated squarewave generator to correspond to the desired streak length. At one extreme, the streak length could correspond to an entire scan of the field and the gated squarewave generator would produce a single pulse.

Likewise, stroboscopic photography can be practiced by fixing the position of the scanner ~i.e., turning off the drive) and triggering the gated squarewave generator 36 in synchronism with the subject sought to be photo-graphed. More particularly, the trigger output of delay 34 or the delayed output of delay 34 can be used to trigger the squarewave generator, i.e., bypass the pulse stretcher 35.

Although the use of TV techniques is well suited to the inventive camera because of its almost "real-time"
response, for increased resolution photograph film can be used. A film holder can be located either in the 25 field 15 after the timing has been adjusted or a beam ~-splitter or mirror added to provide a second field in which the image is painted on a photographically respon-sive film. Of course, film speed, exposure time and illumination intensity will have to be selected to provide optimum images.

While ~e ability of the inventive camera to capture yo97R-n79 ?,~3~8 microsecond images has been emphasized, it should be understood that slower rate images may also be recorded.
For example, by increasing inter-frame time to 2000~sec.
a series of 16 images can be recorded on each video frame with exposure durations up to about 200~sec.

At the other extreme, even shorter exposure times can be produced by replacing the continuous laser - acousto-optic modulator with an ion laser and cavity dumper 51 as shown in Figure 5. These provide a higher power (10 w~ and shorter pulse duration (~ 50 nsec.) so that inter-frame times of 0.5~sec. can be used. Still shorter pulses can be generated in a mode loc~ed ion laser. A commercial mode locked ion laser has pulse durations of 0.2 nsec. separated by 6 nsec~ For the inventive camera, the 6 nsec. inter-frame time re~uires scanner deflection to be adequate in 6 nsec. to separate the images. Sufficiently fast deflection can be obtained with a high frequency resonant scanner which is commer-cially available at about 30 kHz with velocities of

2 x 104 rad/sec. In 6 nsec. a deflection of 10 4 rad is produced. By locating the scanner 14 between objec-tive 27 and subject 13 and using a 10 power objective, effective angular displacement of 10 3 rad is obtained resulting in image displacement of 1 mm~ (at 1 meter).
This is sufficient to distinguish adjacent frames.
Figure 5 illustrates the inventive camera with scanner between subject 13 and objective 27 as discussed above.
The control device 11 is nowrequired to produce a train of pulses at 6 nsec. spacing to trigger the laser 51.
Similar results are more easily obtained with the cavity dumped ion laser with 0.5~sec. pulse spacing since the angular displacement (at 2 x 104 rad/sec) is 10 2 rad.
Accordingly, the objective 27 can be located before scanner 14 or a slower scanner rate can be used.

~r q7~_n7~

Claims (12)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A versatile microsecond camera for recording plural frames of an image which is readily controlled comprising:
switched laser source means for producing a switched beam of illumination;
focusing means for focusing said switched illumination beam on a subject;
mechanical scanner means for redirecting illumination from said subject to sweep over a field;
illumination recording means located in said field for recording illumination from said mechanical scanner means;
and control means responsive to said mechanical scanner means for controlling said switched laser source means.

2. The apparatus of claim 1 wherein said switched laser source means comprises:
a continuous output laser, and switching means in the path of said output for alternately passing and blocking said output in response to said control means.

3. The apparatus of claim 2 in which said switching means comprises an acousto-optic modulator in the path of said illumination, and an aperture located in one of two possible paths of illumination from said acousto-optic modulator and an illumination block in another of said two possible paths, whereby illumination on said one path passes through said aperture and illumination on said another path is blocked.

4. The apparatus of claim 1 wherein said mechanical scanner means comprises:
a resonant electro-mechanical scanner with a reflector for redirecting illumination from said subject, and signal generating means for generating an electrical signal when said reflector achieves a predetermined angular position.

5. The apparatus of claim 1 wherein said mechanical scanner means comprises:
a galvanometer electro-mechanical scanner with a reflector for redirecting illumination from said subject, and signal generating means for generating an electrical signal when said reflector achieves a predetermined angular position.

6. The apparatus of claim 1 wherein said mechanical scanner means includes a reflector swept through an angular movement, and signal generating means for generating an electrical signal corresponding to a predetermined position of said mechanical scanner means and in which said control means includes:
time delay circuit means responsive to said electrical signal. for delaying said signal, pulse stretcher means coupled to said time delay circuit means for delivering a gate signal initiated by said delayed electrical signal and terminated a selected period after initiation, a gated squarewave generator responsive to said gate signal for producing a train of pulses of predetermined duration and repetition rate, and coupling means for coupling said train of pulses to said switched laser source means.

7. The apparatus of claim 6 in which said switched laser source means comprises:
a continuous output laser, an acousto-optic modulator located to receive a beam of illumination from said laser for directing said beam on one of two paths, said coupling means coupled to said acousto-optic modulator, and an aperture located in one of said two paths and an illumination block in said other of said two paths, whereby said laser illumination passes said aperture only when said illumination is directed on said one of said two paths.

8. The apparatus of claim 1 wherein said image recording means comprises:
an image storage tube located in said field, and video recorder means coupled to said image storage tube for periodically permanently recording images from said image storage tube.

9. The apparatus of claim 8 which further includes a video monitor coupled to said video recorder means for displaying images from said video recorder means.

10. The apparatus of claim 8 wherein said image storage tube comprises a vidicon tube.

11. A versatile sub-microsecond camera capable of capturing images of sub-microsecond duration comprising:
ion laser means emitting a pulsed illumination beam of duration less than 100 nsec., microscope means for focusing said pulsed illumination beam on a subject, a resonant mechanical scanner and a reflector driven thereby located in a path of illumination from said subject, a lens for magnifying illumination reflected by said reflector, and image recording means for recording an image located in a path of illumination from said lens.

12. The apparatus of claim 11 wherein said image recording means includes a vidicon tube coupled to a video recorder.